This application describes a five-year research program that investigates individual, social, and structural influences on HIV risk and serostatus among MSM in the four largest cities in Colombia (Bogot, Medelln, Cali, and Barranquilla). This study is of public health significance because it will contribute to knowledge concerning HIV prevalence and risk behavior in an understudied group at high risk for HIV. Moreover, it will evaluate the protection against HIV afforded by circumcision among MSM in Colombia. This application is innovative in its use of a conceptual framework that addresses HIV risk within the social and structural context: in Colombia, there are legal protections of the rights of all individuals, including gay men, while at the same time, there is ongoing civil unrest, forced displacement of large numbers of people, and homonegativity. The aims of the proposed study are 1) to examine structural, social, and individual factors relevant to HIV risk among Colombian MSM in four cities; 2) to estimate prevalence of HIV among MSM in the cities; 3) to test the association between circumcision status and HIV serostatus and to investigate beliefs, knowledge, and attitudes concerning circumcision among Colombian MSM; and 4) to integrate information gained from the various research methods used and to draw conclusions that will guide the design of policies and interventions addressing HIV risk among MSM in Colombia. The research consists of three phases. Phase I involves qualitative research (24 key informant interviews, 18 focus groups, and 28 life history interviews) to explore the context of life in the four cities for MSM, including sexual behavior patterns, social networks, stigma associated with homosexuality and HIV, violence, migration, and displacement,. Life history interviews will be conducted with MSM who have experienced displacement. Phase II involves quantitative research. Rapid oral HIV testing and a quantitative survey instrument (using A-CASI) will be administered to samples of MSM, aged 15 to 49, in the four cities. Data will be used to test a model of HIV risk, to obtain estimates of HIV prevalence in the population of MSM in the four cities, to test for protective effects of circumcision, and to describe attitudes and knowledge of circumcision. The pilot test includes 160 participants; the full administration of the revised survey includes 1000 participants, obtained through respondent-driven sampling. Phase III consists of triangulation of data and dissemination of findings. The contextualized information gained from this research will be useful in HIV prevention efforts for Colombian MSM at the societal, city, community, and individual levels. This application is a five-year research program that investigates individual, social, and structural influences on HIV risk and HIV prevalence among MSM in the four largest cities in Colombia (Bogot, Medelln, Cali, and Barranquilla). In addition, it explores attitudes towards circumcision in the targeted sample.